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Date: Tue, 4 Jun 2019 10:01:18 -0300 From: Jason Gunthorpe <jgg@...pe.ca> To: Catalin Marinas <catalin.marinas@....com> Cc: Andrey Konovalov <andreyknvl@...gle.com>, Linus Torvalds <torvalds@...ux-foundation.org>, linux-arm-kernel@...ts.infradead.org, sparclinux@...r.kernel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org, Vincenzo Frascino <vincenzo.frascino@....com>, Will Deacon <will.deacon@....com>, Mark Rutland <mark.rutland@....com>, Andrew Morton <akpm@...ux-foundation.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Kees Cook <keescook@...omium.org>, Yishai Hadas <yishaih@...lanox.com>, Felix Kuehling <Felix.Kuehling@....com>, Alexander Deucher <Alexander.Deucher@....com>, Christian Koenig <Christian.Koenig@....com>, Mauro Carvalho Chehab <mchehab@...nel.org>, Jens Wiklander <jens.wiklander@...aro.org>, Alex Williamson <alex.williamson@...hat.com>, Leon Romanovsky <leon@...nel.org>, Luc Van Oostenryck <luc.vanoostenryck@...il.com>, Dave Martin <Dave.Martin@....com>, Khalid Aziz <khalid.aziz@...cle.com>, enh <enh@...gle.com>, Christoph Hellwig <hch@...radead.org>, Dmitry Vyukov <dvyukov@...gle.com>, Kostya Serebryany <kcc@...gle.com>, Evgeniy Stepanov <eugenis@...gle.com>, Lee Smith <Lee.Smith@....com>, Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>, Jacob Bramley <Jacob.Bramley@....com>, Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>, Robin Murphy <robin.murphy@....com>, Kevin Brodsky <kevin.brodsky@....com>, Szabolcs Nagy <Szabolcs.Nagy@....com> Subject: Re: [PATCH v2] uaccess: add noop untagged_addr definition On Tue, Jun 04, 2019 at 01:38:00PM +0100, Catalin Marinas wrote: > On Tue, Jun 04, 2019 at 09:28:41AM -0300, Jason Gunthorpe wrote: > > On Tue, Jun 04, 2019 at 02:04:47PM +0200, Andrey Konovalov wrote: > > > Architectures that support memory tagging have a need to perform untagging > > > (stripping the tag) in various parts of the kernel. This patch adds an > > > untagged_addr() macro, which is defined as noop for architectures that do > > > not support memory tagging. The oncoming patch series will define it at > > > least for sparc64 and arm64. > > > > > > Acked-by: Catalin Marinas <catalin.marinas@....com> > > > Reviewed-by: Khalid Aziz <khalid.aziz@...cle.com> > > > Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com> > > > include/linux/mm.h | 11 +++++++++++ > > > 1 file changed, 11 insertions(+) > > > > > > diff --git a/include/linux/mm.h b/include/linux/mm.h > > > index 0e8834ac32b7..dd0b5f4e1e45 100644 > > > +++ b/include/linux/mm.h > > > @@ -99,6 +99,17 @@ extern int mmap_rnd_compat_bits __read_mostly; > > > #include <asm/pgtable.h> > > > #include <asm/processor.h> > > > > > > +/* > > > + * Architectures that support memory tagging (assigning tags to memory regions, > > > + * embedding these tags into addresses that point to these memory regions, and > > > + * checking that the memory and the pointer tags match on memory accesses) > > > + * redefine this macro to strip tags from pointers. > > > + * It's defined as noop for arcitectures that don't support memory tagging. > > > + */ > > > +#ifndef untagged_addr > > > +#define untagged_addr(addr) (addr) > > > > Can you please make this a static inline instead of this macro? Then > > we can actually know what the input/output types are supposed to be. > > > > Is it > > > > static inline unsigned long untagged_addr(void __user *ptr) {return ptr;} > > > > ? > > > > Which would sort of make sense to me. > > This macro is used mostly on unsigned long since for __user ptr we can > deference them in the kernel even if tagged. What does that mean? Do all kernel apis that accept 'void __user *' already untag due to other patches? > So if we are to use types here, I'd rather have: > > static inline unsigned long untagged_addr(unsigned long addr); > > In addition I'd like to avoid the explicit casting to (unsigned long) > and use some userptr_to_ulong() or something. Personally I think it is a very bad habit we have in the kernel to store a 'void __user *' as a u64 or an unsigned long all over the place. AFAIK a u64 passed in from userpace is supposed to be converted to the 'void __user *' via u64_to_user_ptr() before it can be used. (IIRC Some arches require this..) So, if I have a ioctl that takes a user pointer as a u64, and I want to pass it to find_vma, then I do need to write: find_vma(untagged_addr(u64_to_user_ptr(ioctl_u64))) Right? So, IMHO, not accepting a 'void __user *' is just encouraging drivers to skip the needed u64_to_user_ptr() step. At the very worst we should have at least a 2nd function, but, IMHO, it would be better to do a bit more work on adding missing u64_to_user_ptr() calls to get the 'void __user *', and maybe a bit more work on swapping unsigned long for 'void __user *' in various places. Jason
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